Is it possible for a child to have O negative blood type when both parents have A positive?
Yes, it is very possible. O negative means that the child has 2 recessive alleles (genes) for type and 2 recessive alleles for Rh factor. Therefore, his genes would be oo –. This is possible if both parents are heterozygous (have both a dominant and recessive form) for both traits. That would mean Ao +-. The A overrides the o and so does the + vs. -. They show A+ then. They both give the child the o and – ===> oo –, or O-. Statistically, 1/4 of their children can be O type, while the other 3/4 appear as A. Same with + vs -. One fourth would be negative while the other three fourths would be positive.
